In certain applications, it is sometimes necessary to dispense liquids out of a cartridge or similar container and onto a desired target. For example, hot melt adhesives (such as PUR) may be dispensed out of a syringe-like cartridge and onto a desired substrate. In some applications, such as the dispensing of adhesive onto a cell phone assembly, the adhesive must be accurately dispensed into grooves having small dimensions. To perform this operation, conventional jetting dispenser have been utilized. “Jetting” in this context is understood to mean rapidly dispensing minute amounts of viscous material such that each jetted droplet releases from the dispenser. This is accomplished by repeatedly retracting a valve member within a chamber containing the adhesive and extending the valve member until the valve member impacts a valve seat. The impact from the valve member contacting the valve seat causes a minute amount of the viscous material to jet out of an orifice defined by the nozzle.
During a jetting operation, the dispenser must consistently maintain certain temperatures throughout parts of the dispenser through which the adhesive flows in order to ensure uniform adhesive characteristics exist across the system, and likewise optimal jetting performance. However, there also exists a need for materials within the dispenser, and particularly the portion of the dispenser jetting the adhesive, to possess an increased strength to withstand the high level of forces that result from the valve member repeatedly impacting the valve seat. Unfortunately, many such high strength materials have low thermal conductivity. Also, portions of the dispenser, such as pneumatically operated components, function best when isolated from the high temperatures required by the adhesive. Therefore, the conflicting objectives of high strength and high consistent temperatures can result in below optimal dispenser performance.
Additionally, the valve members are often pneumatically or piezoelectrically driven at high velocities and frequencies to jet the adhesive from the dispenser. The travel length of the needle between the retracted and extended positions, also known as the stroke length, is normally a fixed amount dictated by the combination of the valve member, nozzle, and other dispenser geometries. However, different adhesive dispensing applications can be optimally performed using different stroke lengths. As a result, the inability to adjust the stroke length of a valve member limits the utility of a particular dispenser with respect to different varieties of jetting applications.
Therefore, there is a need for a hot melt adhesive dispenser where heat is evenly distributed across the nozzle portion, but isolated from other aspects of the dispenser. There is also a need for a hot melt adhesive dispenser where the stroke length of the valve member is adjustable and can be reliably maintained throughout operation of the dispenser.